Remolding the Interface Stability for Practical Aqueous Zn/I₂ Batteries via Sulfonic Acid-Rich Electrolyte and Separator Design

The electrolyte-electrode interface plays a crucial role in aqueous Zn/I₂ battery and is largely determined by the properties of electrolyte and separator. Here, the synergistic effect of sulfonic acid-rich electrolyte additive and separator impacts the interface stability of Zn/I₂ batteries is comprehensively investigated using operando synchrotron-based Fourier-transform infrared spectroscopy, cryo-electron microscopy, and in situ spectroscopy. As a case study, a cost-effective additive known as lignosulfonic acid sodium (LAS) and a flexible sulfonated polyether sulfone membrane are employed to facilitate the formation of a stable solid electrolyte interface (SEI) on the Zn anode and effectively suppress the shuttle effect. The chemisorption of LAS on Zn, its interaction with Zn²⁺, and the impact on the Zn desolvation process are systematically investigated through both theoretical simulations and operando measurements. Furthermore, the formation of an in situ SEI consisting of ZnS and ZnF₂ is identified, which facilitates the uniform nucleation and planar plating of Zn(002), while effectively suppressing detrimental side reactions. Additionally, visualization experiments and in situ spectroscopy confirm that R−SO₃− groups effectively impede the shuttle process of I³⁻/I⁵⁻ anions through electrostatic repulsion. This work provides valuable insights for designing robust electrolyte interfaces for high-performance aqueous Zn/I₂ batteries.